PT  - JOURNAL ARTICLE
AU  - T Shimada
AU  - F P Guengerich
TI  - Participation of a rat liver cytochrome P-450 induced by pregnenolone 16 alpha-carbonitrile and other compounds in the 4-hydroxylation of mephenytoin.
DP  - 1985 Aug 01
TA  - Molecular Pharmacology
PG  - 215--219
VI  - 28
IP  - 2
4099  - http://molpharm.aspetjournals.org/content/28/2/215.short
4100  - http://molpharm.aspetjournals.org/content/28/2/215.full
SO  - Mol Pharmacol1985 Aug 01; 28
AB  - Mephenytoin 4-hydroxylation, which has been found to be one of the reactions showing genetic polymorphism in humans, has been studied using rat liver microsomes. Pregnenolone 16 alpha-carbonitrile, dexamethasone, troleandomycin, and phenobarbital (but not beta-naphthoflavone) induced the hydroxylation activity to various extents. Mephenytoin itself also increased 4-hydroxylation considerably. Liver microsomes prepared from male rats contained higher mephenytoin hydroxylase activity than preparations isolated from females. These results suggest that a cytochrome P-450 which is inducible by pregnenolone 16 alpha-carbonitrile is involved in the 4-hydroxylation of mephenytoin. We purified cytochrome P-450PCN-E from pregnenolone 16 alpha-carbonitrile-treated rats using modifications of previous methods and compared its 4-hydroxylase activity with other purified rat cytochromes P-450. P-450PCN-E had the highest activity among the 10 purified rat cytochromes P-450 tested and antibodies raised to P-450PCN-E completely inhibited mephenytoin 4-hydroxylase in rat liver microsomes, suggesting the involvement of P-450PCN-E in this reaction. The microsomal concentration of P-450PCN-E, estimated by immunoelectrophoretic blotting analysis, correlated well with the hydroxylase activity in rat liver microsomes (r = 0.906). Mephenytoin induced P-450PCN-E as well as other phenobarbital-inducible cytochromes P-450.